| Intracellular calcium plays an important role in regulating basic physiological functions of cardiac muscles and smooth muscles, Calcium channel blockers have many pharmacological actions, for example, negative inotrope, inhibiting cardiac hypertrophy, improving hemorrheology, vasodilating, endothelium protect and refraining atherosclerosis. Calcium channel blockers are widely used in the treatment hypertension. MN9202 was synthesized by our department and it shows antithrombocic,shock-preventing effects induced by intestinal ischemia-reperfusion in rabbits,In addition, it can inhibit cardiac hypertrophy induced by L-thyroid in rats and lowering blood viscorsity in rats.The effects of MN9202 on the performance of cardiac myocyte contraction and relaxation has not been investigated,and the effects of MN9202 on protein sythesis induced by ET-1 is unkown. .The aim of the present study were to investigate the effects and mechanism of actions of MN9202 and Lacidipine on cardiomyocyte contrctile function,Enzymaticallyisolated cardiomyocytes were used,results of cell level exclude effects of sino-aortic baroreceptor reflex using an optical video system.In additional experiment, we studied endothelium-1 induced protein sythesis in neonatal rat ventricular myocyte in order to elucidate to the mechanism of edothelin-1 induced-induced myocardial hypertrophy. SPECIFIC AIMS:1. To investigate the effects of MN9202,Lacidipine and Iso on cardiomycyte contractile function.2. To study the effects of Forskolin,Methylene blue (inhibitor of guanylyl cyclase) and tetraethylammoniurn choride (inhibitor of calcium activated potassium channel) on the function of cardiac myocyte shortening and relengthening and to analyze the mechanism of actions of MN9202.3. To determine the effects of ET-1 on cardiomyocyte protein synthesis and cardiac hypertrophy,4. .To investigate the effects and it's mechanisms of methyl pentyl, 4-dihydro2, 6-dimethyl-4-(3-nitrophenyl)-3, 5-pridinedicarboxylate (MN9202, a novel dihydropyidine calcium channel blocker) on vascular rings of rat thoracic arteries and to further analyse its mechanism of actions.METHODS:1. Ventricular myocytes were isolated by using collagenase perfusion method. The calcium tolerant ventriclar myocytes were obtained.2. Measurement of myocyte shortening and relengthening were performed in the isolated cardiomyocytes using Ionoptixmoving edges detection video system. We observed the effects of MN9202,Iso and Lacidipine, in order to understand the effects of MN9202 on the myocyte shortening and relengthening and the underlying intracellular signaling mechanism.3. .In cultured neonatal rat cardiac myocyte, MTT methods and total protein measurement were used to evaluate the cell viability and protein sythesis of cardiac myocyte.4. Effects of MN9202 on the tension of vascular strips were studied by in vitro vascular ring perfusion.The effects of TEA were also observed.RESULTS:1. MN9202 and Lacidipine decreased electrically-induced contraction and ph,ph/bl%,+dZ,/dl,-dL/dt.MN9202 and Lacidipine at the concentration of 3 × 10-6 mol/L attenuated the above indexes siganificantly. MN9202(3×10-6 mol/L) decreased ph from( 0.13 ±0.04) μm of baseline to (0.08 ± 0.05) μm(p<0.05), ph/bl% from( 8.6 ± 2.8% )to (5.8±4.3%)(p<0.05), +dL/dt from (1.6 ± 0.5) μm/s to (1.1±0.7)μm/s(p<0.05),-dL/dt from (1.2 ± 0.4) μm/s to (0.8±0.3)μm/s(p<0.05). Lacidipine at dose of 3× 10-6 mol/L decreased ph from (0.13 ± 0.04) μm to (0.07 ± 0.04) μm(p <0.01)ph/bl% from (8.6 ± 2.8%) to (5.6± 3.3%)(p< 0.01), +dL/dt from (1.6 ±0.5) μm/s to (1.0 ± 0.6) μm/s (p < 0.01),-dL/dt from (1.2±0.4) μm/s to (0.7±0.3) μm/s(p<0.01), respectively. Isoproterenol (Iso) at 10-8 mol/L augmented electrically-induced contraction and ph,ph/bl%,+dL/df and -dL/dt by 45%,47%,54%,78% respectively.The effect of Iso (10-8 mol/L) was reduced by MN9202 and Lacidipine at the concentration of3× 10-7 mol/L.The elevation of ±dL/dt and-dL/dt induced by Iso was significantly attenuated by MN9202(p<0.05) and lacidipine (p<0.05) comparing with the control group.2. Forskolin and MB augmented cell shortening and relengtheningwith great significance(p<0.01). Compared with control, Forskolin (10-8 mol/L) increased ph from 0.12±0.03 μm to 0.24±0.06 μm ,ph/bl% from 12±3% to 27±6%,±dL/dt from 1.8±0.5 μm/s to 3.8±0.9 μm/s ,-dL/dt from 1.8±0.22 μm/s to 3.5±0.7 um/s .Above indexes increased 91%, 123%, 110%, 89% respectively,Adenyl cyclase are involved in the positive effects of Forskolin.MB also increased significantly; ph, ph/bl%, +dL/dt and -dL/dt were 0.14 ± 0.04μm, 11±4%, 2.2±0.3μm/s and 2.2 ± 0.6 μm/s respectively.MN9202(3×10(-6) mol/L) siganificantly decreased the Forskolin-iduced increase of +dL/dt and -dL/dt (p<0.05). ,MN9202 attenuated the enhancing effects of ph, ph/bl%, dL/dt and-dL/dt induced by MB and TEA.3. Treatment of cardiac myocytes with ET-1 significantly increased myocyteprotein content (312 ± 30 μg/ml vs 273 ± 20 μg/ml of control, p< 0.05),while treatment with ET-1±NFA , ET-1±che , ET-1±MN9202 , ET-1±Larcidipine and ET-1±PD98059 in cardiac myocyte decreased protein content by 10% (p<0.05), 9%(p<0.05), 8.6% , 13.1%(p<0.05), 6.1%, respectively.4. It was found that MN9202 caused a concentration-dependentrelaxation in rat thoracic arteries which was independent of the endothelium. TEA(10-5mol/L),an antagonist of calcium activated potassium channel(KCa) reduced , but not completely blocked, the vasorelaxing effect of MN9202. CONCLUSION:...
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